Minute to medium sized (1.5-6 mm), slender to stout flies, male and female often differing in colour, the male in particular often all black; one or both sexes partially to all grey or yellow, in some cases with orange, grey or silvery markings, or abdomen bicolourous. Eyes holoptic in the male; antenna with 3 segments, the third of which is largest and bears a long, apical arista. Wing clear or tinged, in some genera the area along the wing margin, in between and around veins Sc and R1 darkened; wing with conspicuous anal lobe; anal vein reaching the wing margin; cell cup ending in an acute angle, often elongate; in most genera vein M forked; crossvein DM-Cu virtually always present (absent in Microsania where crossvein R-M is also lacking). Legs relatively short, stout; first tarsal segment of hind leg in the subfamily Callomyiinae long and cylindrical, usually swollen in the male, slender in the female the subsequent tarsal segments cylindrical; in the subfamily Platypezinae the first tarsal segment of hind leg short, laterally compressed, subsequent tarsal segments laterally compressed as well, in particular in the female.

As far as known the larvae develop on and in mushrooms and bracket fungi. The adults are mainly found in woodland areas, walking about on leaves of trees and shrubs where they feed on honeydew and other organic matter on the leaf surface. The males sometimes fly in swarms; those of Microsania are known as 'smoke flies' since they swarm in the smoke of forest fires (and other fires as well). The larval mode of life of Microsania is not known.